Generally, in lighting devices using light emitting diodes (LEDs), a plurality of LEDs are connected in series to form LED arrays, and the plurality of LED arrays are connected in parallel to form LED modules.
When the plurality of LED arrays having the plurality of LEDs connected in series are connected in parallel and are driven, an operating voltage (Vf) of each LED is changed according to an increase in the operation time thereof, and thus, the current of the LED arrays connected in parallel can be unbalanced.
That is, when an LED is in an abnormal state, an amount of current less than a normal current thereof flows in the LED array including the abnormal LED due to an increase in an operating voltage (Vf) of the LED, or an amount of current more than a normal current flows in the LED array including the abnormal LED due to a decrease in the operating voltage (Vf) of the LED. However, since the set current of a constant current generating source is not changed, a current changed in a degraded LED array is increased or decreased and flows into other LED arrays which are not degraded.
Accordingly, the current of the LED arrays is unbalanced, and thus, brightness by the LED array is generally changed and uniform brightness cannot be maintained. Further, when the current of a specific LED array is increased, the lifetime of the LED can be reduced.
Accordingly, to overcome the above problem, an LED driving circuit, in which a constant current circuit is installed in each of the LED arrays to flow a constant current and an unbalanced current flowing in an LED unit is controlled, is disclosed in Korean Laid-Open Patent No. 2009-0011744.
However, although the LED driving circuit blocks voltages applied to LED columns and reduction of the overall lifetime of the LED is protected, when the LED driving circuit is used in the LED lighting device, the LED lighting device is turned off even when one LED device is broken, and thus, it cannot serve as a lighting device at all.